Optical element obtained by homeotropically orienting liquid crystal molecule, member for liquid crystal display device using the same, and liquid crystal display device

ABSTRACT

An object of the present invention is to provide an optical element which can suppress a production cost, has good heat resistance, uniformly maintains the fixed orientation of a liquid crystal polymer in a wide temperature range, shows a low haze with reliability, and can maintain desired birefringence property with reliability. The present invention relates to an optical element formed by forming, on an upper surface of a base material having light transmittance, at least a birefringence layer having a structure obtained by fixing liquid crystal monomers each having a polymerizable group at a terminal thereof in a state where the monomers are homeotropically oriented, and by removing an additive layer formed on the upper surface of the birefringence layer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical element having abirefringence functional layer. More specifically, the present inventionrelates to an optical element having a birefringence functional layerincluding a birefringence layer obtained by orienting and fixing aliquid crystal molecule, a member for a liquid crystal display deviceusing the optical element, and liquid crystal display device.

2. Description of the Related Art

A liquid crystal display device has found use in a variety of fieldssuch as a television and medical equipment because the device has suchadvantages that the thickness and the weight of the device can bereadily reduced, power consumption can be reduced, and a flicker hardlyoccurs. On the other hand, the device involves a problem which causeslight leak or a tone reversal phenomenon depending on the angle at whicha user views a liquid crystal display screen, that is, a problemreferred to as a narrow viewing angle.

In order to solve the problem, there has been proposed a liquid crystaldisplay device provided with an optical element that controls anoutgoing light emitted from a liquid crystal cell and an incident lightentered into the liquid crystal cell.

For such the liquid crystal display device, there has been proposed anoptical element having a film obtained by orienting and fixing a liquidcrystal molecule in a specific direction as well as a film obtained bysubjecting a triacetylcellulose (TAC) film to uniaxial stretching orbiaxial stretching.

JP 05-142531 A proposes a viewing angle compensation film composed of anematic liquid crystal polymer whose molecular chain is oriented in anormal direction of the film surface and which has a positive intrinsicrefractive index. JP 05-142531 A discloses that the viewing anglecompensation film may be obtained by: forming a vertical alignment layeron the surface of a glass substrate or the like by using analkylsilicone-based or fluoroalkylsilicone-based surface treating agentto produce a cell sealing liquid crystal molecules into the cell; andsubjecting the liquid crystal molecules to photopolymerization.

JP 2002-174724 A proposes a method of producing a liquid crystal layerin which a polymerizable liquid crystal compound is homeotropicallyoriented, the method involving applying the liquid crystal compound to avertical alignment layer formed on a substrate. The method involves theuse of a long-chain alkyl-type dendrimer derivative as an agent forforming a vertical alignment layer. In addition, JP 2002-174724 Adiscloses that a film including a homeotropically oriented liquidcrystal film can be obtained by means of the method, and that the filmcan be used for an optical film such as a retardation film.

JP 2002-174725 A proposes a method of producing a homeotropicallyoriented liquid crystal film involving: applying, to a substrateprovided with no vertical alignment layer, a side-chain type liquidcrystal polymer containing a monomer unit containing a liquid crystalfragment side chain and a monomer unit containing a non-liquid crystalfragment side chain; further homeotropically orienting the liquidcrystal polymer in a liquid crystal state; and fixing the polymer whilethe oriented state is maintained.

JP 2003-121852 A proposes a method of producing a homeotropicallyoriented liquid crystal film involving: forming, on a substrate providedwith no vertical alignment layer, a binder layer and an anchor coatlayer in the stated order from the side of the substrate; applying aside-chain type liquid crystal polymer to the anchor coat layer forhomeotropic orientation; and fixing the polymer while thehomeotropically oriented state is maintained. The method involves theuse of a polymer as a side-chain type liquid crystal polymer capable offorming a homeotropically oriented liquid crystal layer on a substrateprovided with no vertical alignment layer.

SUMMARY OF THE INVENTION

However, the viewing angle compensation film of JP 05-142531 A isobtained after a series of steps of: producing a cell by means of twosubstrates each having an alignment layer; sealing liquid crystalmolecules into the empty cell; vertically orienting the liquid crystalmolecules; and subjecting the liquid crystal molecules tophotopolymerization while maintaining the oriented state of each of themolecules. The viewing angle compensation film of JP 05-142531 A has aproblem in that a production cost significantly increases because thefilm is obtained through a large number of production steps as describedabove.

The method of JP 2002-174724 A requires the use of a special materialcalled a long-chain alkyl-type dendrimer derivative upon production of ahomeotropically oriented liquid crystal layer through the arrangement ofa vertical alignment layer on a substrate. When a homeotropicallyoriented liquid crystal layer is obtained by means of the method, therearises a problem in that a production cost significantly increases.

A homeotropically oriented liquid crystal film obtained by means of themethod described in JP 2002-174725 A is composed of a side-chain typeliquid crystal polymer. Even when the polymer is fixed in ahomeotropically oriented state, its flowability increases withincreasing temperature, and birefringence property is apt to beinfluenced by heat. Therefore, the temperature range in which desiredbirefringence property can be maintained is relatively narrow, and theorientation of a liquid crystal polymer in a part where the liquidcrystal polymer is fixed is apt to be nonuniform. In this case, it isdifficult to use a homeotropically oriented liquid crystal film obtainedby means of the method for a liquid crystal display device requested tohave high heat resistance, so the number of liquid crystal displaydevices each of which is capable of using the liquid crystal film islimited.

In addition, when a homeotropically oriented liquid crystal filmobtained by means of the method is used for a liquid crystal displaydevice, attention must be paid in such a manner that the film is notplaced in a high-temperature environment, so it is difficult to arrangethe film inside the liquid crystal display device. Therefore, ahomeotropically oriented liquid crystal film obtained by means of themethod of JP 2002-174725 A has a problem in that the number of positionswhere the film can be installed in a liquid crystal cell is limited.

A homeotropically oriented liquid crystal film obtained by means of themethod described in JP 2003-121852 A is composed of a side-chain typeliquid crystal polymer, so the method has a problem similar to that ofthe method described in JP 2002-174725 A described above.

In order to solve the above problems, in an optical element having abirefringence layer composed of a liquid crystal polymer layer withfixed orientation, the inventors of the present invention have foundthat a low cost and good heat resistance can be obtained, and a wideviewing angle can be compensated when the birefringence layer is formedby: fixing the orientation of a liquid crystal polymer layer oriented bymeans of a liquid crystal composition containing a crosslinkable,polymerizable liquid crystal monomer and an additive for promoting thehomeotropic orientation of the monomer. However, the finding has beensusceptible to improvement in that an optical element showing a low hazewith reliability and capable of realizing high contrast with reliabilitywhen the optical element is used for a liquid crystal display device isprovided.

The present invention has been made with a view to solving the aboveproblems, and an object of the present invention is to provide anoptical element which: can suppress a production cost; has good heatresistance; uniformly maintains the fixed orientation of a liquidcrystal polymer in a wide temperature range; shows a low haze, to bespecific, a haze of 0.1 or less with reliability; and can maintaindesired birefringence property with reliability. Another object of thepresent invention is to provide an optical element capable of:maintaining the fixed orientation of a liquid crystal molecule in asufficiently uniform state when the optical element installed in aliquid crystal display device; and realizing high contrast withreliability. Another object of the present invention is to provide aliquid crystal display device having a wide viewing angle.

That is, the gist of the present invention is as follows:

(1) An optical element including: a base material having lighttransmittance; and a birefringence functional layer including at least abirefringence layer, wherein: the birefringence layer has a structureobtained by fixing liquid crystal monomers each having a polymerizablegroup at a terminal thereof in a state where the monomers arehomeotropically oriented; the birefringence layer contains an additivefor promoting the homeotropic orientation of the liquid crystal monomer;and no additive layer constituted by the additive is present on theupper surface of the birefringence layer;

(2) An optical element according to item (1), wherein the birefringencefunctional layer consists of a vertical alignment layer formed on anupper surface of the base material and the birefringence layer formed onan upper surface of the vertical alignment layer;

(3) An optical element according to item (2), wherein at least onecomponent for promoting homeotropic orientation of a liquid crystalmonomer in the vertical alignment layer is used for the additive;

(4) An optical element according to item (1), wherein the liquid crystalmonomers constituting the birefringence layer are oriented while showinga substantially uniform tilt angle;

(5) An optical element according to item (1), wherein a coloring layeris formed on one of a position between the base material and thebirefringence functional layer and a position on an upper surface of thebirefringence functional layer;

(6) A member for a liquid crystal display device including: twolaminated structures each including a layer having light transmittance;and a liquid crystal layer in which liquid crystal is sealed, the liquidcrystal layer being interposed between the two laminated structures,wherein the optical element according to item (1) is formed in at leastone of the laminated structures;

(7) A member for a liquid crystal display device according to item (6),wherein the birefringence layer in the optical element is formed to bepositioned on a side of the liquid crystal layer in the member for aliquid crystal display device;

(8) A liquid crystal display device having a multilayer structure, thedevice including: polarizing plates with liquid crystal interposedtherebetween; and a layer composed of an electrode portion for changingorientation of a liquid crystal layer through application of a voltage,wherein the member for a liquid crystal display device according to item(6) is used; and

(9) A liquid crystal display device having a multiplayer structure, thedevice including: polarizing plates with liquid crystal interposedtherebetween; and a layer composed of an electrode portion for changingorientation of a liquid crystal layer through application of a voltage,wherein the member for a liquid crystal display device according to item(7) is used.

According to the optical element of the present invention, uponformation of a birefringence layer, liquid crystal monomers constitutingthe birefringence layer are vertically oriented through the addition ofan additive for promoting the homeotropic orientation of the monomer, sonot only a liquid crystal monomer close to the side of a substrate butalso a liquid crystal monomer apart from the substrate can behomeotropically oriented favorably and uniformly. Therefore, an opticalelement having a birefringence layer forming, in the thickness directionof the birefringence layer, a state where liquid crystal ishomeotropically oriented with improved uniformity can be obtained. Theabove-described optical element of the present invention can be used asan element for controlling the polarized state of light such as anelement for controlling a phase difference or an optical compensationelement. In addition, the optical element can impart a phase differencecontrol function with improved finesse because the uniformity oforientation is improved.

In addition, the above liquid crystal monomers are polymerizable, so abirefringence layer can be formed of a liquid crystal polymer obtainedby crosslinking the liquid crystal monomers that have beenhomeotropically oriented. The optical element of the present inventionincluding a birefringence layer having the above crosslinked structurecan be used even for an optical instrument to be used in an environmentwhere a temperature is relatively apt to be high such as the inside of avehicle because the optical element has high heat resistance and itsbirefringence property is hardly influenced by heat. Furthermore, theoptical element can be arranged even in a liquid crystal panel installedin an optical instrument because the optical element has relatively highheat resistance. In particular, according to the present invention inwhich the above crosslinked structure is a three-dimensional crosslinkedstructure, the above effects can be obtained with improved significance.

Furthermore, in the birefringence layer in the present invention, anadditive layer to be formed on the surface of the birefringence layer(that is, a surface opposite to the side of a substrate in thebirefringence layer) is removed, so the optical element of the presentinvention including the birefringence layer can reduce a haze to 0.1 orless with reliability. As a result, a phase difference can be controlledwith improved favorableness, and a degree of transparency can beincreased.

The above optical element can be laminated and formed integrally on amember constituting a liquid crystal panel, and an optical instrumentcan be designed without the separate arrangement of any member (phasedifference control member) such as a film for controlling a phasedifference. Separately arranging a phase difference control memberrequires the fixing of the member by means of an adhesive or the like.However, the optical element of the present invention can eliminate theneed for such adhesive, and can reduce the possibility of, for example,the scattering of light due to an adhesive.

When the optical element of the present invention is provided with acoloring layer, and the resultant is used for a liquid crystal displaydevice, the need to arrange a phase difference control member separatefrom a member having the coloring layer is eliminated, so the thicknessof the liquid crystal display device can be reduced.

The production cost of the optical element of the present invention canbe easily suppressed because the birefringence layer can be formedthrough a relatively easy process involving: applying, to the uppersurface of a base material or the upper surface of a vertical alignmentlayer formed by applying a composition liquid for the upper film of thebase material, a birefringence layer composition liquid; orientingliquid crystal; and crosslinking the liquid crystal.

A member for a liquid crystal display device using the optical elementcan improve a phase difference control function, and a liquid crystaldisplay device provided with the characteristics of the optical elementsuch as a reduction in possibility of light scattering due to anadhesive can be produced by means of the member.

In addition, the thickness of a liquid crystal display device using theoptical element can be reduced as compared to that of a liquid crystaldisplay device formed by means of a conventional optical compensationfilm. In addition, the liquid crystal display device can effectivelyutilize light, has good contrast, and can provide a wide viewing angle.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a conceptual view for explaining an optical element of thepresent invention;

FIG. 2A is a conceptual view showing a state where a resin compositioncontaining liquid crystal monomers and an additive is applied to theupper surface of a substrate so that the liquid crystal monomers arehomeotropically oriented, FIG. 2B is a conceptual view showing a statewhere the homeotropically oriented liquid crystal monomers arethree-dimensionally crosslinked, and FIG. 2C is a conceptual viewshowing the fact that an additive layer is formed on a surface by bakinga birefringence layer;

FIG. 3 is a schematic view showing the sectional structure of theoptical element of the present invention;

FIG. 4A is a schematic view showing the sectional structure of anoptical element obtained by providing a substrate with a functionallayer and FIG. 4B is a schematic view showing the sectional structure ofanother example of the optical element obtained by providing a substratewith a functional layer;

FIG. 5 is a schematic view showing the sectional structure of theoptical element on which an additional functional layer is laminated;

FIG. 6A is a schematic view showing the sectional structure of anoptical element provided with a coloring layer, FIG. 6B is a schematicview showing the sectional structure of another example of the opticalelement provided with a coloring layer, and FIG. 6C is a schematic viewshowing another example of the sectional structure of the opticalelement provided with a coloring layer;

FIG. 7A is a schematic view showing a member for a liquid crystaldisplay device provided with an optical element of a first embodimentand FIG. 7B is a schematic view showing a member for a liquid crystaldisplay device having the optical element of the first embodiment formedin such a manner that a birefringence layer is positioned between asubstrate and a liquid crystal layer;

FIG. 8 is a schematic view showing a member for a liquid crystal displaydevice provided with an optical element of a third embodiment; and

FIG. 9A is a schematic view showing a liquid crystal display device of afirst embodiment and FIG. 9B is a schematic view showing a liquidcrystal display device of a second embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the best mode for carrying out the present invention willbe described with reference to the drawings.

FIG. 1 is a conceptual view showing an optical element 1 of the presentinvention. The optical element 1 is formed of: a base material 2; abirefringence layer 4 on the upper surface of the base material 2, thebirefringence layer 4 being obtained by three-dimensionally crosslinkinghomeotropically oriented liquid crystal monomers 3 and by fixing theorientation. The birefringence layer 4 contains an additive 5 forpromoting the homeotropic orientation of the liquid crystal monomers,and the additive is present at an interface between the base material 2and any one of the liquid crystal monomers 3, or is present between thetwo adjacent liquid crystal monomers 3. The birefringence functionallayer in the optical element 1 shown in FIG. 1 is formed only of thebirefringence layer 4. However, as described later, the birefringencefunctional layer in the present invention is not limited thereto, andmay be constituted by a vertical alignment layer and a birefringencelayer.

A process for forming the optical element 1 will be schematicallyexplained. At first, as shown in FIG. 2A, a birefringence layercomposition liquid containing the liquid crystal monomers 3 that can bethree-dimensionally crosslinked and the additive 5 is applied to thebase material 2 so that the liquid crystal monomers 3 arehomeotropically oriented on the base material 2. Next, for example,active radiation is applied so that the liquid crystal monomers 3 arethree-dimensionally crosslinked as shown in FIG. 2B and thehomeotropically oriented liquid crystal monomers 3 are fixed on the basematerial 2. At this time, the additive 5 is present at an interfacebetween the base material 2 and any one of the liquid crystal monomers3, or is present between the two adjacent liquid crystal monomers 3.After that, when the formed article obtained in FIG. 2B is baked forimproving the heat resistance and adhesiveness of the birefringencelayer 4, an additive layer 6 is formed on the surface of thebirefringence layer 4 as a result of aggregation of the additive 5 asshown in FIG. 2C. In addition, the additive layer 6 is estimated to beformed as a result of bleeding of part of the additive 5 present betweenthe monomers 3 to the surface of the birefringence layer through bakingbecause the additive layer 6 has a small specific gravity of theadditive 5.

The inventors of the present invention have found that the presence ofthe additive layer 6 is responsible for an increase in haze of anoptical element, and reduces the desired phase difference controlfunction in the birefringence layer 4. On the basis of the finding, theyhave completed the optical element 1 including the birefringence layer 4from which the additive layer 6 has been removed. The additive layer 6can be removed by means of a generally known method such as abrasion oretching. The presence of the additive layer 6 can be confirmed on thebasis of the fact that the surface layer of the optical element iswhitish. Therefore, the removal of the additive layer 6 can be confirmedby removing the whitish surface layer by means of, for example,abrasion. Alternatively, the following procedure may be adopted. Thatis, the thickness of the additive layer is determined depending on thedesign of the optical element and a production condition such as thedose of active radiation or a baking treatment. Therefore, in an opticalelement to be produced on the basis of desirable design and under adesirable production condition, the thickness of an additive layer to beformed is measured in advance, and the surface of the optical element isdeleted by means of, for example, abrasion or etching by the thicknessso that the additive layer is removed.

Hereinafter, the optical element of the present invention will bedescribed in more detail.

An optical element 1 a of the present invention shown in FIG. 3 isconstituted by positioning the base material 2 having lighttransmittance, a vertical alignment layer 10, the birefringence layer 4having the additive 5 therein in the stated order. In the opticalelement 1 a, a birefringence functional layer is constituted by thevertical alignment layer 10 and the birefringence layer 4. However, thebirefringence functional layer in the present invention is not limitedthereto. When the additive 5 promotes the homeotropic orientation ofeach of the liquid crystal monomers 3 sufficiently, a vertical alignmentlayer is not always formed.

The base material 2 includes a layer composed of a substrate 2 a havinglight transmittance. The base material may be constituted by a structurecomposed of a single substrate layer, may be constituted by a multilayerstructure obtained by superimposing a large number of substrates 2 a, ormay be constituted by laminating a functional layer 2 b provided with apredetermined function on the layer composed of the substrate 2 a. Forexample, the base material 2 may be constituted by forming thefunctional layer 2 b on each surface of the substrate 2 a (FIG. 4A), maybe constituted by forming the functional layer 2 b on one surface of thesubstrate 2 a (FIG. 4B), or may be constituted by forming the functionallayer 2 b inside the substrate 2 a (not shown).

The present invention shown in each of FIGS. 4 to 9 omits thedescription about an additive present in the birefringence layer 4 forconvenience.

An optically isotropic substrate is preferably used for the substrate 2a. A substrate partially provided with a light-shielding region or thelike is also available. In addition, the light transmittance of thesubstrate 2 a can be appropriately selected. To be specific, a plate,sheet, or film formed of a transparent, inorganic material ortransparent, organic material can be used.

Examples of the transparent, inorganic material include glass, silicon,and quartz. Of those, quartz is preferable because it has small thermalexpansibility, good dimensional stability, and excellent workability ina high-temperature heating treatment. In particular, when a color filterof the present invention is used for a liquid crystal display, no-alkaliglass free of any alkali component in the glass is preferably used for asubstrate.

Meanwhile, an example of the transparent organic material can includeone made of: acryl such as polymethylmethacrylate; polyamide,polyacetal, polybutylene terephthalate, polyethylene terephthalate,polyethylene naphthalate, triacetyl cellulose, orsyndiotactic/polystyrene; polyphenylene sulfide, polyether ketone,polyetherether ketone, a fluororesin, or polyether nitrile;polycarbonate, a modified polyphenylene ether, polycyclohexene, or apolynorbornene-based resin; or polysulphone, polyether sulphone,polyacrylate, polyamide imide, polyether imide, or thermoplasticpolyimide. In addition, one made of a common plastic can be used. Inparticular, a uniaxial oriented film or a biaxial oriented film, a TACfilm having retardation in plane, or the like can be used as a film. Thethickness of the substrate 10 is not particularly limited, but thethickness is generally near 0.05 mm to 1.5 mm depending on applications.

The functional layer 2 b is a layer having a function of changing thestate of light, and differs from the birefringence layer 4. Specificexamples of the functional layer include: a horizontal alignment layerin which a liquid crystal molecule is horizontally oriented; a verticalalignment layer in which a liquid crystal molecule is verticallyoriented; a coloring layer; a reflecting plate for reflecting light; anda polarizing plate. In addition, the functional layer 2 b may be notonly arranged on the entire surface of the substrate 2 a, but alsopartially on the surface of the substrate 2 a.

The vertical alignment layer 10 is formed by means of a liquidcontaining a component for promoting the homeotropic orientation of aliquid crystal monomer such as soluble polyimide, polyamic acid, asurfactant, a coupling agent, or a combination of them as a layercomposition liquid by: applying the layer composition liquid by means ofa method such as flexographic printing or spin coating; and curing theapplied liquid.

The thickness of the vertical alignment layer 10 is preferably in therange of about 0.01 to 1 μm. A thickness of the vertical alignment layer10 of less than 0.01 μm may make it difficult to homeotropically orientliquid crystal. In addition, a thickness of the vertical alignment layer10 in excess of 1 μm may cause the vertical alignment layer 10 itself toirregularly reflect light to significantly reduce the lighttransmittance of the optical element.

Specific examples of the layer composition liquid containing solublepolyimide, polyamic acid, or the like include: SE-7511 and SE-1211manufactured by NISSAN CHEMICAL INDUSTRIES, LTD.; and JALS-2021-R2manufactured by JSR.

Polyimide having a long-chain alkyl group is preferably used for formingthe vertical alignment layer 10 because the thickness of thebirefringence layer 4 formed in the optical element can be selected froma wide range.

When the vertical alignment layer 10 is formed by means of a layercomposition liquid containing a surfactant and/or a coupling agent, thesurfactant has only to be capable of homeotropically orientingpolymerizable liquid crystal having a rod-like molecular shape;provided, however, that a surfactant or coupling agent of which avertical alignment layer to be heated together with the birefringencelayer is formed must have such heat resistance that it is not decomposedeven at the transition temperature at which liquid crystal undergoes atransition to a liquid crystal phase because the liquid crystal must beheated to the transition temperature upon formation of the birefringencelayer. In addition, a surfactant or coupling agent of which a verticalalignment layer to be in contact with the birefringence layer is formedpreferably has a high affinity for an organic solvent into which liquidcrystal is dissolved because the liquid crystal is dissolved into theorganic solvent upon formation of the birefringence layer. Thesurfactant may be a nonionic surfactant, a cationic surfactant, ananionic surfactant, or any other surfactant without any limitation aslong as such condition as described above is satisfied. Only a singlekind of surfactant may be used, or multiple kinds of surfactants may beused in combination. As in the case of the surfactant, the kind of thecoupling agent is not limited, and multiple kinds of coupling agents maybe used in combination.

Examples of the surfactant can include (a) a surfactant having an alkylchain or long alkyl side chain, (b) a surfactant having an alkyl chainor long alkyl side chain at least part of which is substituted byfluorine, and (c) a surfactant having a side chain containing a fluorineatom. In particular, a surfactant having strong water repellency orstrong oil repellency is preferably used for homeotropically orientingpolymerizable liquid crystal even when the thickness of thebirefringence layer 4 is increased.

Specific examples of the surfactant having strong water repellency oroil repellency include (i) lecithin, (ii)octadecyldimethyl(3-trimethoxysilylpropyl)ammonium chloride, (iii)hexadecyl amine, (iv) ADEKAMINE 4DAC-85 (trade name of a surfactantmanufactured by Asahi Denka Co., Ltd.), (v) DRYPON 600E (trade name of asurfactant manufactured by NICCA CHEMICAL), (vi) DRYPON Z-7 (trade nameof a surfactant manufactured by NICCA CHEMICAL), and (vii) NK GuardNDN-7E (trade name of a surfactant manufactured by NICCA CHEMICAL).

A specific example of the coupling agent includes a silane-couplingagent obtained by hydrolyzing a silane compound such asn-octyltrimethoxysilane, n-octyltriethoxysilane, decyltrimethoxysilane,decyltriethoxysilane, n-dodecyltrimethoxysilane,n-dodecyltriethoxysilane, octadecyltrimethoxysilane, oroctadecyltriethoxysilane.

In particular, a coupling agent which strongly homeotropicaly orientsliquid crystal molecules of the birefringence layer 4 can include afluorine-based silane coupling agent.

A specific example of the coupling agent includes a fluorine-basedsilane coupling agent obtained by hydrolyzing a fluorine-based silanecompound such as perfluoroalkylsilane, pentafluoroalkylsilane,pentafluorophenyl trimethoxysilane, pentafluorophenyl triethoxysilane,pentafluoropheylpropyl trimethoxylsilane, pentafluorophenylpropyltriethoxysilane, trifluoropropyl trimethoxysilane, trifluoropropyltriethoxysilane, 1H,1H,2H,2H,-perfluorodecyl trimethoxysilane,1H,1H,2H,2H,-perfluorodecyl triethoxysilane, 1H,1H,2H,2H,-perfluoroocyltrimethoxysilane, 1H,1H,2H,2H,-perfluoroocyl triethoxysilane,3-(peptafluoroisopropoxy)propyl trimethoxysilane, or3-(peptafluoroisopropoxy)propyl triethoxysilane.

Next, the birefringence layer 4 will be described. As shown in FIG. 3,the birefringence layer 4 is formed to have a crosslinked polymerstructure obtained by crosslinking the liquid crystal monomers 3 eachhaving a slightly elongated molecular shape in a state where themonomers are homeotropically oriented.

A bonding hand showing a state where the liquid crystal monomers 3 arebound to each other is not shown in any one of FIGS. 3 and 5 forconvenience.

In the birefringence layer 4, the additive 5 is present at an interfacebetween any one of the liquid crystal monomers 3 and the verticalalignment layer 10 (or the base material 2 when the vertical alignmentlayer 10 is not formed), and is present between the two adjacent liquidcrystal monomers 3. The above-described component for promoting thehomeotropic orientation of a liquid crystal polymer such as polyimide, asurfactant, a coupling agent, or a combination of them can be used asthe additive 5. The additive 5 can be arbitrarily selected from thegroup consisting of polyimide, a surfactant, a coupling agent, and acombination of them when a birefringence functional layer is formed onlyof the birefringence layer 4 without the formation of the verticalalignment layer 10. On the other hand, the same component as a componentconstituting the vertical alignment layer 10 (that is, polyimide, asurfactant, a coupling agent, or a combination of them) can be used forthe additive 5 when a birefringence functional layer is formed byforming the vertical alignment layer 10 and by forming the birefringencelayer 4 after the formation of the layer 10.

The degree of crosslinking of the liquid crystal monomers 3 of thebirefringence layer 4 is preferably about 80 or more, or more preferablyabout 90 or more. A degree of crosslinking of the liquid crystalmonomers of less than 80 may be unable to maintain uniform orientationsufficiently.

In the birefringence layer 4, the tilt angles of the liquid crystalmonomers 3 each serving as a unit constituting a crosslinked polymerstructure are desirably such that the tilt angle of a liquid crystal(for example, a liquid crystal monomer 3 a) molecule at the positionclosest to a boundary between the birefringence layer 4 and the verticalalignment layer 10 and the tilt angle of a liquid crystal (for example,a liquid crystal monomer 3 b) molecule at the position most distant fromthe above liquid crystal molecule in the thickness direction (thedirection along arrows L and M) of the birefringence layer aresubstantially equal to each other (see FIG. 3). In this case, the tiltangles of the respective liquid crystal monomers 3 in the birefringencelayer 4 are substantially uniform in the thickness direction. As aresult, uniform homeotropic orientation can be obtained in thebirefringence layer 4. Furthermore, the tilt angles of the liquidcrystal monomers 3 in the birefringence layer 4 are more preferably madeequal to each other in the thickness direction. In particular, the tiltangles of the respective liquid crystal monomers 3 constituting thebirefringence layer 4 can be made substantially equal to each otherbecause the birefringence layer 4 has the additive 5 for promoting thehomeotropic orientation of each of the liquid crystal monomers 3.

The birefringence layer 4 provides light to be incident on thebirefringence layer 4 (incident light) with retardation in associationwith the anisotropy of the refractive index of each of the liquidcrystal monomers 3 constituting the layer 4. The retardation is anoptical path difference between ordinary light and extraordinary lightoccurring in the incident light. The magnitude of the retardation isrepresented as the product of birefringence Δn (a difference between therefractive index no of the ordinary light and the refractive index ne ofthe extraordinary light) and the thickness d of the birefringence layer4. Therefore, from the viewpoint of the fact that the retardation andorientation property of the birefringence layer 4 are determined by thebirefringence Δn and the thickness, the birefringence Δn is preferablyabout 0.03 to 0.20, or more preferably about 0.05 to 0.15. An of lessthan 0.03 requires an increase in thickness of a phase differencecontrol functional layer in order that sufficient retardation may beobtained. An excessively large thickness may make it impossible for aliquid crystal polymer close to an interface on the side of the air tomaintain specified orientation. In addition, the thickness of the phasedifference control functional layer is preferably 0.1 μm to 5 μm. Athickness of the phase difference control functional layer of less than0.1 μm may fail to exert a sufficient phase difference control function.The magnitude of the retardation of the birefringence layer 4 to beobtained as described above is preferably 1 nm or less, more preferably0.1 nm or less, or ideally zero.

The birefringence can be measured by measuring the retardation and thethickness. Any one of commercially available devices such as KOBRA-21series (manufactured by Oji Scientific Instruments) can be used formeasuring the retardation. A measurement wavelength at the time ofmeasurement is preferably in the visible light range (380 nm to 780 nm),and is more preferably around 550 nm at which relative luminousefficiency is largest. A commercially available device such as a styluslevel difference meter DEKTAK (Sloan) can be used for measuring thethickness.

The liquid crystal monomers 3 constituting the birefringence layer 4 canuse monomers each liquid crystal state of which can be fixed at roomtemperature, more specifically, monomers each of which has anunsaturated double bond in its molecular structure and can becrosslinked in a liquid crystal state (including polymerizable liquidcrystal). In particular, one having an unsaturated double bond at aterminal of a molecule is used as the polymerizable liquid crystal.Examples of such crosslinkable liquid crystal monomer material includeCompounds (I) exemplified in the following formulae [Chem 1] to [Chem10] and Compounds (II) included in a general chemical formularepresented by [Chem 11]. One kind of Compounds (I) exemplified in theformulae [Chem 1] to [Chem 10] or a mixture of two or more kinds ofthem, one kind of Compounds (II) included in the general chemicalformula represented by [Chem 11] or a mixture of two or more kinds ofthem, or a mixture obtained by combining them can be used as the liquidcrystal monomer material that can be used in the present invention. Inthe case of a liquid crystal monomer included in the general chemicalformula [Chem 11], X representing a long alkyl chain positioned at eachend of an aromatic ring is preferably 4 to 6 (integer).

(In the formula, X represents an integer of 4 to 6.)

The birefringence layer 4 in the optical element of the presentinvention can be formed by: applying, to the vertical alignment layer 10(or the base material 2), a birefringence layer composition liquidobtained by blending the liquid crystal monomers 3 as described abovewith a solvent and the additive 5 to form a coating film;homeotropically orienting the liquid crystal monomers in the coatingfilm; and crosslinking the liquid crystal monomers 3 while maintainingthe homeotropically oriented state. The birefringence layer 4 may beformed through patterning on the vertical alignment layer 10 by means ofany one of various printing methods or a photolithography method. When abirefringence functional layer is formed only of the birefringence layer4 without the formation of the vertical alignment layer 10, a coatingfilm can be formed by applying the birefringence layer compositionliquid directly to the base material 2.

The solvent is not particularly limited as long as it is capable ofdissolving liquid crystal, and any one of various organic solvents suchas toluene can be used; provided, however, that the solvent preferablyallows the birefringence layer composition liquid having a uniformthickness to be applied to the vertical alignment layer 10.

The loading of the liquid crystal monomers 3 in the birefringence layercomposition liquid is preferably in the range of 10 to 50 wt % althoughthe preferable range varies depending on, for example, an applicationmethod, a thickness, and the kind of the solvent. In the birefringencelayer composition liquid, a compounding ratio (weight ratio) of theadditive 5 to the liquid crystal monomers 3 is 1/7 to ⅓.

The additive 5 in the present invention is not particularly limited aslong as it is a compound capable of promoting the homeotropicorientation of a liquid crystal monomer which is of the above-describedrod-like molecular shape and which is polymerizable. Examples of theadditive 5 can include the above-described polyimide, a surfactant, acoupling agent, and combination of them. Although the loading of theadditive 5 to be used varies depending on, for example, a material forthe base material, the thickness of the birefringence layer, and theorientation restraining force of the additive to be used, a preferableloading range is, for example, as described below.

When soluble polyimide or polyamic acid is loaded as the additive 5 intothe birefringence layer composition liquid, the loading of the additiveis in the range of preferably 12.5 to 25 wt %, or more preferably 15 to22.5 wt % with respect to the total amount of polymerizable liquidcrystal. A loading of polyamic acid serving as the additive 5 of lessthan 12.5 wt % may make it difficult to obtain a birefringence layercomposition that is sufficiently uniformly oriented. A loading in excessof 25 wt % may reduce light transmittance.

When a coupling agent or a surfactant is loaded as the additive 5, theloading of the additive is in the range of preferably 0.001 to 5 wt %,more preferably 0.01 to 1.0 wt %, or still more preferably 0.05 to 0.5wt % with respect to the total amount of the polymerizable liquidcrystal.

A combination of multiple compounds each of which is capable ofpromoting the homeotropic orientation of the above liquid crystalmonomers can be used as the additive 5. The loading of the combinationcan be appropriately determined because the loading varies depending on,for example, a material for the base material, the thickness of thebirefringence layer, and the orientation restraining force of theadditive to be used. For example, when a combination of a surfactant anda silane coupling agent is used as the additive 5, a mass ratio of thesurfactant to the solid content of the silane coupling agent ispreferably appropriately selected from the range of about 1/100 to 1/1although the mass ratio varies depending on, for example, theorientation restraining force of the silane coupling agent to be used.The diluent of a commercially available vertical alignment layersolution may also be used as the additive 5. In this case, thecomposition ratio of the vertical alignment layer solution can bedirectly adopted as the loading of the additive 5.

The refractive index layer composition liquid may be added with aphotopolymerization initiator or a sensitizer as required.

Examples of the photopolymerization initiator include: benzyl (orbibenzoyl); benzoin isobutyl ether; benzoin isopropyl ether;benzophenone; benzoylbenzoic acid; methyl benzoyl benzoate;4-benzoyl-4′methyldiphenylsulfide; benzyl methyl ketal;dimethylaminomethyl benzoate; 2-n-butoxyethyl-4-dimethylamino benzoate;isoamyl p-dimethylamino benzoate; 3,3′-dimethyl-4-methoxybenzophenone;methylobenzoyl formate;2-methyl-1-(4-(methylthio)phenyl)-2-morpholinopropane-1-one;2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butane-1-one;1-(4-dodecylphenyl)-2-hydroxy-2-methylpropane-1-one;1-hydroxycyclohexylphenylketone;2-hydroxy-2-methyl-1-phenylpropane-1-one;1-(4-isopropylphenyl)-2-hydroxy-2-methylpropane-1-one;2-chlorothioxanthone; 2,4-diethylthioxanthone;2,4-diisopropylthioxanthone; 2,4-dimethylthioxanthone;isopropylthioxanthone; and 1-chloro-4-propoxythioxanthone.

When a photopolymerization initiator is loaded into the birefringencelayer composition liquid, the loading of the photopolymerizationinitiator is in the range of 0.01 to 10 wt %. The loading of thephotopolymerization initiator is preferably such that damage to theorientation of a liquid crystal molecule is reduced to the extentpossible. In view of this point, the loading is in the range ofpreferably 0.1 to 7 wt %, or more preferably 0.5 to 5 wt %.

When a sensitizer is loaded into the birefringence layer compositionliquid, the loading of the sensitizer can be appropriately selected fromthe range in which the orientation of a liquid crystal molecule is notlargely damaged. To be specific, the loading is selected from the rangeof 0.01 to 1 wt %.

In addition, only one kind of photopolymerization initiator (orsensitizer) may be used, or two or more kinds of photopolymerizationinitiators (or sensitizers) may be used in combination.

Hereinafter, a method of producing the optical element of the presentinvention will be described in more detail. In the followingdescription, an optical element is used, which has a vertical alignmentlayer formed by means of a surfactant and a birefringence layer formedby means of a birefringence layer composition liquid containing, as anadditive, a surfactant serving as the same component as that of thevertical alignment layer.

At first, a layer composition liquid containing a surfactant is preparedby means of such material as described above. The liquid is applied tothe upper surface of the base material 2 having light transmittance bymeans of a method such as flexographic printing or spin coating toproduce a coating film for a vertical alignment layer. Furthermore, thecoating film for a vertical alignment layer is cured to produce avertical alignment layer-formed base material in which the verticalalignment layer is formed on the base material.

Next, liquid crystal monomers each serving as polymerizable liquidcrystal and a surfactant are dissolved into a solvent to prepare abirefringence layer composition liquid. The liquid is applied to thevertical alignment layer-formed base material to produce a coating filmfor a birefringence layer.

At first, the birefringence layer composition liquid is applied to thevertical alignment layer-formed base material by means of any one ofmethods such as various printing methods (including die coating, barcoating, slide coating, and roll coating) and spin coating. The basematerial to which the birefringence layer composition liquid has beenapplied is dried to form a coating film for a birefringence layer. Atthis time, the base material to which the birefringence layercomposition liquid has been applied can be air-dried under atmosphericpressure.

When the surface of the vertical alignment layer-formed base materialhas high water repellency or high oil repellency, the wettability of thesurface of the vertical alignment layer-formed base material to whichthe birefringence layer composition liquid is to be applied may beimproved in advance through UV washing or a plasma treatment to theextent that liquid crystal can be homeotropically oriented.

Next, the liquid crystal monomers in the coating film for abirefringence layer are homeotropically oriented.

To be specific, the coating film for a birefringence layer is heated sothat the temperature of the coating film for a birefringence layerbecomes equal to or higher than the temperature (liquid crystal phasetemperature) at which the liquid crystal in the coating film becomes aliquid crystal phase and lower than the temperature at which the liquidcrystal in the coating film becomes an isotropic phase (liquid phase).Thus, the liquid crystal is homeotropically oriented. At this time, amethod of heating the coating film for a birefringence layer is notparticularly limited. A method involving placing the coating film in aheating atmosphere is permitted. A method involving heating the coatingfilm with infrared light is also permitted.

A method of homeotropically orienting the liquid crystal is not limitedto the above method. For example, depending on a liquid crystal monomerin the coating film for a birefringence layer and the state of thecoating film, a method involving drying the coating film for abirefringence layer under reduced pressure or a method involvingapplying an electric field or a magnetic field to the coating film for abirefringence layer from a predetermined direction can be employed forrealizing the homeotropic orientation.

When the coating film for a birefringence layer is dried under reducedpressure so that a liquid crystal monomer is homeotropically oriented,establishing a decompressed state can bring the coating film for abirefringence layer into a supercooled state. As a result, the coatingfilm for a birefringence layer can be additionally cooled to roomtemperature while the homeotropically oriented state of a liquid crystalmonomer in the coating film is maintained. In this case, a state wherethe liquid crystal is homeotropically oriented is maintained efficientlyuntil the liquid crystal monomers are subjected to a crosslinkingreaction.

Next, the homeotropically oriented liquid crystal is subjected to acrosslinking reaction in the coating film for a birefringence layer sothat the orientation is fixed.

The crosslinking reaction progresses through the irradiation of thecoating film for a birefringence layer with light having a wavelength towhich a liquid crystal monomer is sensitive. At this time, thewavelength of light with which the coating film for a birefringencelayer is irradiated is appropriately selected in accordance with thekind of a liquid crystal monomer in the coating film. Light with whichthe coating film for a birefringence layer is irradiated is not limitedto monochromatic light, or may be light having a certain wavelengthrange including the wavelength to which the liquid crystal is sensitive.To be specific, active radiation such as ultraviolet light is generallyapplied.

The crosslinking reaction of the liquid crystal is preferably performedwhile the coating film for a birefringence layer is heated to atemperature lower than the temperature at which the liquid crystalundergoes a phase transition from a liquid crystal phase to an isotropicphase by 1 to 10° C. This action can reduce the disturbance of thehomeotropic orientation of the liquid crystal at the time of thecrosslinking reaction. In addition, in view of the foregoing, thetemperature at which the crosslinking reaction is performed is morepreferably a temperature lower than the temperature at which the liquidcrystal undergoes a phase transition from a liquid crystal phase to anisotropic phase by 3 to 6° C.

The crosslinking reaction of liquid crystal may be performed by means ofa method involving irradiating a coating film for a birefringence layerwith light having a wavelength to which the liquid crystal is sensitivewhile heating the coating film up to a liquid crystal phase temperaturein an inert gas atmosphere. The above method is preferable because theliquid crystal is crosslinked in the inert gas atmosphere, and thedisturbance of the homeotropic orientation of a liquid crystal moleculeat a position distant from a vertical alignment layer can be suppressedas compared to the case where the liquid crystal is crosslinked in anair atmosphere.

Alternatively, the crosslinking reaction of the liquid crystal may beperformed by means of a method involving the steps of: irradiating thecoating film for a birefringence layer with light having a wavelength towhich the liquid crystal is sensitive while heating the coating film upto the liquid crystal phase temperature in an inert gas atmosphere or inthe air atmosphere, to thereby partially progress the crosslinkingreaction (referred to as a partial crosslinking step); cooling thecoating film for a birefringence layer to the temperature (Tc) at whichthe liquid crystal becomes a crystal phase after the partialcrosslinking step; and additionally irradiating the coating film for abirefringence layer with light having a wavelength to which the liquidcrystal is sensitive in this state, to thereby progress and complete thecrosslinking reaction. The above-mentioned temperature Tc is thetemperature at which the liquid crystal becomes a crystal phase in thecoating film for a birefringence layer before the progress of thecrosslinking reaction.

In the partial crosslinking step, the crosslinking reaction proceeds tothe extent that the homeotropic orientation of the liquid crystal in thecoating film for a birefringence layer is maintained even when thecoating film is cooled to the temperature Tc. Therefore, the degree towhich the crosslinking reaction proceeds in the partial crosslinkingstep is appropriately selected depending on, for example, the kind ofthe liquid crystal in the coating film for a birefringence layer and thethickness of the coating film. In the partial crosslinking step, thecrosslinking reaction is preferably caused to proceed in such a mannerthat the degree of crosslinking of the liquid crystal becomes about 5 to50.

Upon completion of the crosslinking step, a base material, a verticalalignment layer, a liquid crystal layer including a birefringence layercomposed of liquid crystal monomers which are homeotropically orientedand the orientation of each of which is fixed as a result ofcrosslinking of the monomers is formed.

After the crosslinking step, the optical element is baked. The bakingstep is an important step because the heat resistance and adhesivenessof the birefringence layer can be improved with the step. However, onthe other hand, the baking causes a surfactant used as an additive tobleed and agglomerate so that an additive layer is formed on the surfaceof the birefringence layer.

The baking step can be performed by: installing the optical elementobtained by completing the crosslinking step in, for example, an ovenheated to a certain temperature; and heating the optical element. Forexample, the baking step can be performed in the air atmosphere andunder atmospheric pressure by means of a “circulating hot air ovenKLO-60M” manufactured by AS ONE CORPORATION. A baking temperature and abaking time can be appropriately determined depending on, for example,the thickness of the optical element, in particular, the thickness ofthe birefringence layer, and the kind of a liquid crystal monomer to beused. The baking time is preferably in the range of 0.5 hour to 2.5hours (both inclusive), and the baking temperature is preferably in therange of 200° C. to 250° C. (both inclusive). A baking time in thebaking step in excess of 2.5 hours may cause the yellowing or the likeof the optical element so that the permeability of the optical reduces.In addition, a baking time of less than 0.5 hour may reduceadhesiveness, heat resistance, and a degree of cure so that sufficientdurability cannot be obtained.

After the baking, the additive layer constituted by the surfactant isremoved. A method of removing the additive layer is not particularlylimited as long as the additive layer can be removed with the method.Examples of such method include: a method involving grinding the layerby means of a grinding attachment; a method involving removing the layerthrough a solvent treatment by means of a spin coater; and a methodinvolving removing the layer by means of a plasma etching device. Inremoval of the additive layer, a part of the birefringence layer whichis positioned below the additive layer is also removed, to causereduction in the phase difference control function of the birefringencelayer. Therefore, the method which is able to adjust the amount of thelayer to be removed is preferable. The thickness of the additive layeris determined by, for example, the dose of light in the crosslinkingstep, the kind of the additive, and the amount of the additive to beadded. Therefore, the thickness to be removed may be determined byacknowledging in advance the thickness of the additive layer to beformed upon design and production of the optical element.

As described above, the optical element of the present invention has abirefringence layer obtained by fixing liquid crystal monomers that arein homeotropically oriented states, and an additive layer formed on theupper surface of the side of the birefringence layer is removed.Accordingly, an excellent phase difference control function can beexerted, and a haze can be reduced to 0.1 or less with reliability.Therefore, the optical element has an improved degree of transparency inits thickness direction. In addition, the occurrence of a portion with adiscontinuous refractive index in the thickness direction of the opticalelement is suppressed, so the scattering of light passing through theoptical element in the thickness direction can be suppressed.

In the optical element 1 in the present invention, the birefringencelayer 4 has a structure obtained by crosslinking and polymerizing theliquid crystal monomers 3 while maintaining the homeotropically orientedstates of the monomers. Suppose xyz orthogonal coordinates with thethickness direction of the birefringence layer 4 as a z axis. In thiscase, a refractive index nx in an x axis direction and a refractiveindex ny in a y axis direction have substantially the same value, and arefractive index nz in the z axis direction can be made larger than therefractive indices nx and ny. Therefore, in the optical element 1, thebirefringence layer 4 can be a layer having birefringence property withwhich the refractive indices satisfy the relationship of nz>nx=ny, thatis, a layer having an optical axis in its thickness direction (z axisdirection) and uniaxial birefringence property. The layer 4 can becaused to function as a so-called “+C plate” and as a member having aphase difference control function with which the retardation of lightcan be optically compensated.

The optical element of the present invention has liquid crystal fixed ina homeotropically oriented state. Therefore, the optical element can beused as, for example, an element for controlling the polarized state oflight such as an element for controlling a phase difference or anoptical compensation element. In consideration of the fact that thescattering of light can be suppressed as described above, the opticalelement can be an element having a function of controlling a phasedifference with improved finesse. As a result, a liquid crystal displaydevice capable of reducing light leak with improved finesse can beproduced by means of the optical element. Furthermore, a liquid crystaldisplay device with an expanded viewing angle, improved contrast, andsuppressed color unevenness in its liquid crystal display screen can beproduced.

The birefringence property of the optical element 1 is hardly influencedby heat because the birefringence layer 4 has a crosslinked structure.

The production cost of the optical element 1 can be easily suppressedbecause the birefringence layer 4 can be formed through a relativelyeasy process involving: applying a layer composition liquid to the basematerial 2 to produce the vertical alignment layer 10; applying abirefringence layer composition liquid to the layer 10; orienting liquidcrystal; and crosslinking the liquid crystal.

Furthermore, the optical element 1 has the birefringence layer 4 formedby means of a birefringence layer composition liquid containing theadditive 5 for promoting the homeotropic orientation of each of theliquid crystal monomers 3. As a result, the birefringence layer 4 of theoptical element 1 can bring the degree of homeotropic orientation ofeach of the liquid crystal monomers 3 at positions apart from the basematerial 2 or the vertical alignment layer 10 close to the degree ofhomeotropic orientation of each of the liquid crystal monomers 3adjacent the base material 2 or the vertical alignment layer 10. As aresult, a state where the liquid crystal is homeotropically orientedwith improved uniformity can be formed in the thickness direction of thebirefringence layer 4.

The optical element 1 can be laminated and formed integrally on a memberconstituting a liquid crystal panel. As a result, an optical instrumentcan be designed without the separate arrangement of any phase differencecontrol member.

The optical element of the present invention may include a functionallayer having a function of changing the state of light and differentfrom the birefringence layer which is laminated on at least one of theexternal surface and substrate surface of the optical element of a firstembodiment of the present invention (hereinafter referred to as a“second embodiment”).

The optical element of the second embodiment will be described by takingthe case where a layer different from the birefringence layer inbirefringence property is formed as a functional layer on the externalsurface of the optical element of the first embodiment as an example. Asshown in, for example, FIG. 5, the optical element of the secondembodiment can be formed in such a manner that a functional layer 2 c ispositioned between the base material 2 and the vertical alignment layer10.

The functional layer 2 c in the optical element of the second embodimentmay be a layer (hereinafter referred to as the “different birefringencelayer”) having birefringence property different from that of thebirefringence layer in the first embodiment (+C plate).

To be specific, the different birefringence layer may be a layer havingbirefringence property with which the above-described refractive indicessatisfy the relationship of nz=nx<ny or nz=ny<nx, that is, a layerfunctioning as a so-called “+A plate”. Alternatively, the layer may be alayer having birefringence property with which the above-describedrefractive indices satisfy the relationship of nz<nx=ny, that is, alayer functioning as a so-called “−C plate”.

The above-described layer functioning as the so-called “+A plate” can beobtained by: forming a coating film for forming a horizontal alignmentlayer of, for example, a resin material capable of horizontallyorienting liquid crystal on the surface of a base material or on abirefringence layer; subjecting the surface of the coating film forforming a horizontal alignment layer to a rubbing treatment or a lightorientation treatment to produce a horizontal alignment layer; applyinga solution prepared by dissolving liquid crystal into a solvent to thehorizontal alignment layer; and fixing the solution in a homogeneouslyoriented state.

The above-described layer functioning as the so-called “−C plate” can beobtained by: applying a solution prepared by dissolving liquid crystaland a chiral agent into a solvent to the surface of a base material orto a birefringence layer; and fixing the solution.

The chiral agent is added for orienting a liquid crystal molecule in ahelical fashion. When the liquid crystal molecule takes a helical pitchin an ultraviolet region, a specific reflected color occurs owing to aselective opposition phenomenon. Therefore, the loading of the chiralagent is preferably such amount that a helical pitch in which theselective opposition phenomenon occurs in the ultraviolet region isobtained.

The optical element of the second embodiment is obtained by laminatinglayers different from each other in birefringence property. When aliquid crystal display device provided depending on the optical elementis produced, upon acknowledgement of light that has passed through theliquid crystal display device, a change in magnitude of retardationdepending on the position at which an observer views the passed lightcan be efficiently suppressed.

The optical element of the present invention includes a coloring layerwhich may be formed in the optical element of the first or secondembodiment of the present invention (hereinafter referred to as a “thirdembodiment”).

The optical element of the third embodiment will be described by takingthe case where a coloring layer is formed as a functional layer on thesubstrate of a base material as an example (FIG. 6A).

FIG. 6A is a schematic view showing the sectional structure of anexample of the optical element of the third embodiment.

An optical element 1 b has a substrate 2 a as a base material, and acoloring layer 11 is formed on one surface of the substrate. Thecoloring layer 11 is composed of a coloring pixel portion 12 throughwhich visible light in a predetermined wavelength region passes and alight-shielding portion 13 (which may be referred to as a black matrixor a BM).

The coloring pixel portion 12 is formed by arranging coloring pixelsthrough which light beams having the wavelength ranges of the respectivecolors (red, green, and blue) pass (referred to as a red coloring pixel12R, a green coloring pixel 12G, and a blue coloring pixel 12B) in apredetermined pattern. The arrangement mode of the red coloring pixel12R, the green coloring pixel 12G, and the blue coloring pixel 12B eachconstituting the coloring pixel portion 12 can be selected from variousarrangement patterns such as a stripe type pattern, a mosaic typepattern, and a triangle type pattern.

Coloring pixels through which light beams having the wavelength rangesof the complementary colors for the respective colors pass can be usedinstead of those coloring pixels (12R, 12G, and 12B).

The coloring pixel portion 12 is formed by patterning the coating filmof a coloring material dispersion liquid prepared by dispersing acoloring material for each of the coloring pixels (12R, 12G, and 12B) ofthe respective colors into a solvent into a predetermined shape by meansof, for example, a photolithography method.

The coloring pixel portion 12 can also be formed by applying a coloringmaterial dispersion liquid for each of the coloring pixels (12R, 12G,and 12B) of the respective colors in a predetermined shape as well as aphotolithography method.

The light-shielding portion 13 prevents the coloring pixels (12R, 12G,and 12B) from being superimposed on one another, and fills a gap betweenadjacent coloring pixels to suppress the leak of light (leaked light)from a position between the adjacent coloring pixels. In addition, thelight-shielding portion suppresses the light degradation or the like ofan active device when the optical element is used for a member for aliquid crystal display device of an active matrix drive system.

Therefore, the light-shielding portion 13 is formed in such a mannerthat regions corresponding to the positions at which the coloring pixelsare arranged on the surface of the substrate 2 a are compartmentalizedfor the respective coloring pixels (12R, 12G, and 12B) in a plan view.In addition, the coloring pixels (12R, 12G, and 12B) of the respectivecolors are arranged in accordance with the positions at which thecoloring pixels are formed in the regions on the surface of thesubstrate 2 a compartmentalized by the light-shielding portion 13 insuch a manner that the regions are covered with the coloring pixels in aplan view.

The light-shielding portion 13 can be formed by patterning a metal thinfilm having light-shielding property or light-absorbing property such asa metal chromium thin film or a tungsten thin film in a predeterminedshape onto a substrate surface. In addition, the light-shielding portioncan be formed by printing an organic material such as a black resin in apredetermined shape.

The coloring layer 11 is not limited to such layer including coloringpixels for multiple colors as described above, and may be constituted bymeans of a coloring pixel for a single color. In this case, the coloringlayer 11 may be free of the light-shielding portion 13.

The optical element of the third embodiment has been described by takingthe case where all of the coloring pixel portion 12 and thelight-shielding portion 13 constituting the coloring layer 11 arearranged on a substrate as an example. However, the present invention isnot limited thereto. As shown in FIG. 6B, the optical element may beformed by: forming only the light-shielding portion 13 in the coloringlayer on a substrate to provide a base material; laminating the verticalalignment layer 10 and the birefringence layer 4 on the base material;and arranging the coloring pixel portion 12 on the resultant. In suchcase, the additive layer on the surface of the birefringence layer 4must be removed before the arrangement of the coloring pixel portion 12.

According to the optical element of the third embodiment shown in FIG.6A, the coloring layer 11 on the substrate 2 a can be covered with thebirefringence layer 4. In this case, the heat resistance of the coloringpixel portion 12 to be covered with the vertical alignment layer 10 orwith the birefringence layer 4 can be improved because the heatresistance of the birefringence layer 4 is relatively high.

When the optical element is provided with a coloring layer, as shown inFIG. 6C, the coloring layer 11 may be laminated on the birefringencelayer 4 in addition to the above case. In such case, the additive layeron the surface of the birefringence layer 4 must be removed before thecoloring layer 11 is formed.

Next, a member for a liquid crystal display device using the opticalelement of the first or second embodiment (which may be referred to as amember for a liquid crystal display device of a first embodiment) willbe described in detail.

FIGS. 7A and 7B are schematic views each showing an example of themember for a liquid crystal display device of the present invention.

Description will be given of the case where the optical element of thefirst embodiment is formed on one side of a laminated structure as anexample of a member for a liquid crystal display device.

As shown in FIG. 7A, a member 50 a for a liquid crystal display deviceincludes two laminated structures 14 (14 a and 14 b) each having lighttransmittance, and a liquid crystal layer 17 is formed between thelaminated structures 14 a and 14 b.

The laminated structure 14 a in which no optical element is formedincludes a substrate 16 and an alignment layer 15 formed on thesubstrate 16. The laminated structure 14 b in which the optical element1 a is formed includes the respective layers (2, 10, and 4) of which theoptical element 1 a is formed and the alignment layer 15. In addition,the laminated structures 14 are arranged in such a manner that thealignment layers 15 and 15 of both the laminated structures 14 a and 14b are opposite to each other.

The liquid crystal layer 17 is formed by sealing liquid crystal into agap between the laminated structures 14 a and 14 b. The liquid crystalto be sealed is appropriately selected.

The liquid crystal layer 17 is formed as described below. That is, aclearance gap (cell gap) between the laminated structures 14 a and 14 barranged so as to be opposite to each other with a slight gap betweenthem is fixed by means of a spacer 18 (such as a spherical spacer or acolumnar spacer). Then, a space portion compartmentalized between thelaminated structures 14 a and 14 b is formed by means of a sealant (athermosetting resin). Filling the space portion with a liquid crystalmaterial results in the sealing of liquid crystal, thereby the liquidcrystal layer 17 is formed.

Each of the alignment layers 15 is a horizontal alignment layer forhorizontally orienting the liquid crystal in the liquid crystal layer 17formed between the laminated structures 14 or a vertical alignment layerfor vertically orienting the liquid crystal. Which one of a horizontalalignment layer and a vertical alignment layer is used as the alignmentlayer can be appropriately selected.

The member 50 a for a liquid crystal display device of the firstembodiment is provided with the optical element 1 a including thebirefringence layer 4. Therefore, a liquid crystal display device havingrelatively high heat resistance can be obtained at a low cost. Inaddition, there is no need to interpose a phase difference control filmseparately for optical compensation, so the thickness of the member fora liquid crystal display device can be reduced. Moreover, the need foran adhesive material that must be applied upon interposition of thephase difference control film is eliminated, so display property can beadditionally improved. As a result, a transmission liquid crystaldisplay device that can find use in a variety of applications can easilybe provided at a low cost.

The member for a liquid crystal display device may be constituted byforming an optical element in each of the laminated structures oppositeto each other in addition to the above-described example.

The member for a liquid crystal display device may be such that theoptical element 1 a is formed in such a manner that the birefringencelayer 4 is positioned between the base material 2 and the liquid crystallayer 17 like the member 50 a for a liquid crystal display device shownin FIG. 7B. In this case, the birefringence layer 4 can be preventedfrom being exposed to the external surface of the member for a liquidcrystal display device. As a result, the possibility that thebirefringence layer 4 is damaged by an acting force from the outside inthe course of the use of the member can be suppressed.

Next, a member for a liquid crystal display device using the opticalelement of the third embodiment (hereinafter referred to as the memberfor a liquid crystal display device of a second embodiment) will bedescribed.

FIG. 8 is a schematic view showing an example of a member 50 b for aliquid crystal display device of the second embodiment of the presentinvention. In the member for a liquid crystal display device, the casewhere the optical element of the third embodiment is formed on one sideof a laminated structure is taken as an example.

The member 50 b for a liquid crystal display device of the secondembodiment includes two laminated structures 14 a and 14 c each havinglight transmittance as in the case of the member for a liquid crystaldisplay device of the first embodiment. The liquid crystal layer 17 isformed between the laminated structures 14 a and 14 c. The laminatedstructure 14 a in which the optical element 1 b is not formed isobtained by forming the alignment layer 15 on the substrate 16.

In the member 50 b for a liquid crystal display device, the laminatedstructure 14 c in which the optical element 1 b is formed has thealignment layer 15 arranged in such a manner that the birefringencelayer 4 is positioned between the alignment layer and the substrate 2 a.The laminated structures 14 a and 14 c are arranged in such a mannerthat the alignment layers 15 and 15 are opposite to each other.

The optical element 1 b of the third embodiment is formed in thelaminated structure 14 c, and a protective layer 21 that serves toflatten the surface on which the alignment layer 15 is laminated andformed is arranged between the optical element 1 b and the alignmentlayer 15. Additionally the protective layer 21 is arranged to protectthe birefringence layer 4 while additionally improving the chemicalresistance, heat resistance, resistance to indium tin oxide (ITO), andthe like of the birefringence layer 4.

The protective layer 21 can be formed of: any one of variousphoto-setting or thermosetting resins such as an acrylic resin, anepoxy-based resin, and polyimide; or a two-liquid setting resin. Theprotective layer can be formed by means of a method such as spincoating, printing, or photolithography depending on a material for thelayer. The thickness of the protective layer 21 is in the range of 0.3to 5.0 μm, or preferably 0.5 to 3.0 μm.

A member for a liquid crystal display device having such structure canbe used for, for example, a liquid crystal panel for color display in areflection liquid crystal display device.

Next, a liquid crystal display device 100 a using the member for aliquid crystal display device of the first embodiment (liquid crystaldisplay device of a first embodiment) will be described. In Examples, inparticular, the case where the liquid crystal display device is of anin-plain switching mode (IPS mode) system will be described as anexample.

As shown in FIG. 9A, polarizing plates 31 and 31 are arranged on bothexternal surfaces of the member 50 a for a liquid crystal displaydevice. In addition, a flat electrode portion 25 interposed and formedbetween the substrate 16 and the alignment layer 15 each constitutingthe laminated structure 14 a of the member 50 a for a liquid crystaldisplay device, and a light irradiation portion 30 are arranged.

The polarizing plates 31 and 31 are stuck to both external surfaces ofthe member 50 a for a liquid crystal display device. Alternatively, boththe polarizing plates 31 and 31 may be arranged in such a manner thatthey establish a crossed nicol relationship, or may be arranged in sucha manner that they establish a parallel nicol relationship.

The flat electrode portion 25 is composed of a liquid crystal drivingelectrode portion 26 and a common electrode portion 27 whichelectrically corresponds to the liquid crystal driving electrode portion26 and which faces the portion 26. Both the liquid crystal drivingelectrode portion 26 and the common electrode portion 27 are arrangedbetween the same substrate 16 and the liquid crystal layer 17. The flatelectrode portion 25 changes the orientation of a liquid crystalmolecule in the liquid crystal layer 17 through the application of avoltage.

The liquid crystal driving electrode portion 26 includes: many liquidcrystal driving electrodes 26 a arranged in a matrix manner; and aflattening film 26 b for flattening a surface.

Each of the many liquid crystal driving electrodes 26 a arranged in amatrix manner constitutes a single pixel for each region in which theliquid crystal driving electrode is arranged. The liquid crystal drivingelectrodes 26 a travel longitudinally across substantially the centralportions of the corresponding pixels in a plan view. Each of the liquidcrystal driving electrodes 26 a is formed of a transparent electrodematerial such as indium tin oxide (ITO).

The common electrode portion 27 includes common electrodes 27 a each ofwhich is capable of generating an electric field in a gap between thecommon electrode 27 a and the corresponding liquid crystal drivingelectrode 26 a. In addition, a protective layer 27 b with which thecommon electrodes are covered so as to be out of physical contact withthe liquid crystal driving electrode portion 26 is formed in the portion27. The common electrodes 27 a are arranged as described below. That is,two of the common electrodes 27 a are arranged on both sides of eachpixel train formed of the respective liquid crystal driving electrodes26 a arranged in a matrix manner so as to correspond to the train.

Each of the common electrodes 27 a can be formed of a metal such astantalum (Ta) or titanium (Ti).

In the liquid crystal display device 10 a, a voltage is applied to theliquid crystal layer for each pixel, and the amount of light passingthrough a polarizing plate out of light received from the lightirradiation portion 30 is controlled for each pixel. Then, in the liquidcrystal display device, light emitted to the outside through thepolarizing plate for each pixel entirely forms an image.

The liquid crystal display device 100 a of the first embodiment can beused also as an on-vehicle liquid crystal display device havingrelatively high heat resistance and exposed to arelatively-high-temperature environment because the member 50 a for aliquid crystal display device has the birefringence layer 4 having acrosslinked structure with improved uniformity of homeotropicorientation. In addition, a liquid crystal display device can beprovided at a low cost because the production cost of the flat electrodeportion 25 can be easily suppressed. In addition, in a conventionalliquid crystal display device, a film (phase difference control film)for correcting a phase difference has been stuck as a separate body bymeans of an adhesive or the like for correcting a narrow viewing angle.In contrast, the liquid crystal display device 100 a eliminates the needfor such film, so a thickness for arranging an adhesive is not needed.As a result, the thickness of the device can be reduced. In addition,the possibility of the irregular reflection, absorption, or the like oflight due to the adhesive can be reduced.

Furthermore, a liquid crystal display device 100 b using the member fora liquid crystal display device of the second embodiment (liquid crystaldisplay device of a second embodiment) will be described. In Examples,in particular, the case where the liquid crystal display device is of anactive matrix system will be described as an example (FIG. 9B).

In the liquid crystal display device 100 b, the polarizing plates 31 and31 are arranged on both side surfaces of the member 50 b for a liquidcrystal display device. In addition, an electrode portion 29 isinterposed between the substrates 16 and 2 a constituting the laminatedstructures of the member 50 b for a liquid crystal display device, andthe light irradiation portion 30 is provided for the device 100 b.

The electrode portion 29 is composed of pixel electrode portions 26arranged for the respective pixels and a common electrode portion 28which electrically corresponds to each of the pixel electrode portions26 and which faces the portion 26. The pixel electrode portions 26 andthe common electrode portion 28 are arranged in such a manner that theliquid crystal layer 17 is interposed between them.

The pixel electrode portions 26 are formed as described below. The pixelelectrodes 26 a are arranged in a matrix manner so that each of them isin one-to-one correspondence with any one of the coloring pixels 12R,12G, and 12B in its thickness direction. Each pixel electrode portion isprovided with: a switching circuit portion (not shown) provided for eachpixel electrode; a signal line 26 c and a scanning line (not shown)electrically connected to the switching circuit portion; an interlayerinsulator (not shown) for electrically separating the signal line 26 cand the scanning line; a protective film 26 d for electricallyseparating the signal line 26 c and the pixel electrode; and theflattening film 26 b with which the protective film 26 d and the pixelelectrode 26 a are covered for flattening a surface.

In the electrode portion 29, the scanning line and the signal line 26 care arranged so as to intersect each other in a lattice fashion betweenadjacent pixel electrodes. The scanning line/the signal line 26 c iscovered along its longitudinal direction with the interlayerinsulator/the protective film 26 d.

Each of the scanning line and the signal line is formed of a metal suchas tantalum (Ta) or titanium (Ti). The interlayer insulator is formedof, for example, an electrically insulating substance such as a siliconoxide. In addition, the protective film is formed of a silicon nitrideor the like.

Each of the many pixel electrodes arranged in a matrix mannerconstitutes a single pixel for each region in which the pixel electrodeis arranged.

Each of the pixel electrodes is formed of a transparent electrodematerial such as indium tin oxide (ITO).

The switching circuit portion is arranged in correspondence with a pixelelectrode, and electrically connects the pixel electrode with thescanning line and the signal line. The switching circuit portion issupplied with an electrical signal from the scanning line to control thestate of energization between the signal line and the pixel electrode.Specific examples of the switching circuit portion include activedevices such as a three-terminal type device (for example, a thin-filmtransistor) and a two-terminal type device (for example, a metalinsulator metal (MIM) diode).

The common electrode portion 28 is formed of a transparent electrodematerial such as indium tin oxide (ITO) into a film shape.

The liquid crystal display device 100 b of the second embodimenteliminates the need to arrange a phase difference control film as aseparate body as in the case of the liquid crystal display device 100 aof the first embodiment. As a result, the thickness of the device can bereduced. In addition, an adhesive to be used upon sticking of a film isnot needed, so the possibility of the irregular reflection or absorptionof light due to an adhesive material can be reduced.

EXAMPLES

Next, the present invention will be described in more detail by way ofexamples and comparative examples.

(Pretreatment for Glass Base Material)

A no-alkali glass plate having a low expansion coefficient (1737 glassmanufactured by Corning Incorporated and measuring 100 mm long by 100 mmwide by 0.7 mm thick) was prepared as abase material subjected to anappropriate washing treatment to be clean.

(Preparation of Vertical Alignment Layer Solution)

A JALS-2021-R2 (manufactured by JSR) was used as a vertical alignmentlayer solution containing polyamic acid or the like as a component forpromoting the homeotropic orientation of a polymerizable liquid crystalmonomer, and was diluted with γ-butyrolactone to 50%.

(Preparation of Birefringence Layer Composition Liquid)

A birefringence layer composition liquid to be used for the formation ofa birefringence layer was prepared as described below. 20 parts byweight of the compound shown in [Chem 11] (provided that X represents 6)as a polymerizable liquid crystal monomer molecule showing a nematicliquid crystal phase, 0.8 part by weight of a photopolymerizationinitiator (“IRGACURE 907” manufactured by Ciba-Geigy), 59.2 parts byweight of chlorobenzene as a solvent, and 20 parts by weight of asolution prepared by diluting the above solution for forming a verticalalignment layer JALS-2021-R2 with diethylene glycol dimethyl ether to12.5% were mixed to prepare a birefringence layer composition liquid.

(Preparation of Coloring Resist)

A pigment-dispersed photoresist was used as a coloring material for eachof: a black matrix; and red (R), green (G), and blue (B) coloringpixels. The pigment-dispersed photoresist is obtained by: adding beadsto a dispersion liquid composition (containing a pigment as a coloringmaterial, a dispersant, and a solvent); dispersing the resultant bymeans of a dispersing device for 3 hours; and mixing the dispersionliquid from which the beads have been removed and a clear resistcomposition (containing a polymer, a monomer, an additive, an initiator,and a solvent). The composition is shown below. A PAINT SHAKER(manufactured by ASADA TEKKO) was used as the dispersing device.

The composition of each photoresist is shown below. (Photoresist forblack matrix) Black pigment 14.0 parts by weight(TMBLACK#9550manufacturedbyDainichiseikaColor&Chemicals Mfg. Co., Ltd.)Dispersant 1.2 parts by weight (Disperbyk 111 manufactured byBYK-Chemie) Polymer 2.8 parts by weight (VR60 manufactured by SHOWAHIGHPOLYMER CO., LTD.) Monomer 3.5 parts by weight (SR399 manufacturedby Sartomer Company, Inc.) Additive 0.7 part by weight (L-20manufactured by Soken Chemical & Engineering Co. Ltd.) Initiator 1.6parts by weight(2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone- 1) Initiator0.3 part by weight (4,4′-diethylaminobenzophenone) Initiator 0.1 part byweight (2,4-diethylthioxanthone) Solvent 75.8 parts by weight(ethyleneglycol monobutylether) (Photoresist for red (R) coloring pixel)Red pigment 4.8 parts by weight (C.I. PR254 (CROMOPHTAL DPP Red BPmanufactured by Ciba Specialty Chemicals)) Yellow pigment 1.2 parts byweight (C.I. PY139 (Paliotol Yellow D1819 manufactured by BASF))Dispersant 3.0 parts by weight (Solsperse 24000 manufactured by ZenekaColours) Monomer 4.0 parts by weight (SR399 manufactured by SartomerCompany, Inc.) Polymer 1 5.0 parts by weight Initiator 1.4 parts byweight (IRGACURE 907 manufactured by Nihon Ciba-Geigy K.K.) Initiator0.6 part by weight(2,2′-bis(o-chlorophenyl)-4,5,4′,5′-tetraphenyl-1,2′-biimidazol) Solvent80.0 parts by weight (propyleneglycol monomethylether acetate)(Photoresist for green (G) coloring pixel) Green pigment 3.7 parts byweight (C.I. PG7 (SeikaFastGreen5316PmanufacturedbyDainichiseika Color &Chemicals Mfg.Co., Ltd.)) Yellow pigment 2.3 parts by weight (C.I. PY139(Paliotol Yellow D1819 manufactured by BASF)) Dispersant 3.0 parts byweight (Solsperse 24000 manufactured by Zeneka Colours) Monomer 4.0parts by weight (SR399 manufactured by Sartomer Company, Inc.) Polymer 15.0 parts by weight Initiator 1.4 parts by weight (IRGACURE 907manufactured by Nihon Ciba-Geigy K.K.) Initiator 0.6 part by weight(2,2′-bis(o-chlorophenyl)-4,5,4′,5′-tetraphenyl-1,2′-biimidazol) Solvent80.0 parts by weight (propyleneglycol monomethylether acetate)(Photoresist for blue (B) coloring pixel) Blue pigment 4.6 parts byweight (C.I. PB15: 6 (Heliogen Blue L6700F manufactured by BASF)) Violetpigment 1.4 parts by weight (C.I. PV23 (Hostaperm RL-NF manufactured byClariant)) pigment derivative 0.6 part by weight (Solsperse 12000manufactured by Zeneka Colours) Dispersant 2.4 parts by weight(Solsperse 24000 manufactured by Zeneka Colours) Monomer 4.0 parts byweight (SR399 manufactured by Sartomer Company, Inc.) Polymer 1 5.0parts by weight Initiator 1.4 parts by weight (IRGACURE 907 manufacturedby Nihon Ciba-Geigy K.K.) Initiator 0.6 part by weight(2,2′-bis(o-chlorophenyl)-4,5,4′,5′-tetraphenyl-1,2′-biimidazol) Solvent80.0 parts by weight (propyleneglycol monomethylether acetate)

It should be noted that the polymer 1 described herein is obtained byadding 16.9 mol % of 2-methacryloyloxy ethylisocyanate with respect to100 mol % of a copolymer consisting of benzylmethacrylate: styrene:acrylic acid: 2-hydroxyethyl methacrylate=15.6:37.0:30.5:16.9 (molarratio), and has a weight average molecular weight of 42,500.

Example 1

The vertical alignment layer solution was patterned onto the uppersurface of a glass base material by means of a flexographic printingmethod to form a film having a thickness of 600 Å. The resultant wasbaked at 180° C. for 1 hour, so a vertical alignment layer was formed onthe glass base material. Next, the base material on which the verticalalignment layer had been formed was installed in a spin coater (tradename “1H-360S” manufactured by MIKASA), and the birefringence layercomposition liquid prepared in advance was applied to the upper surfaceof the alignment layer by means of spin coating in such a manner that athickness after drying would be about 1.5 μm. In this example, a spincoating method was adopted as a method of applying a liquid crystalsolution. However, a method of applying a liquid crystal solution is notlimited thereto. For example, die coating, slit coating, and an approachas a result of combination of them can be appropriately selected. Thesame holds true for the examples to be described later. Next, the basematerial to which the liquid crystal solution had been applied washeated on a hot plate at 100° C. for 3 minutes so that the remainingsolvent was removed and a liquid crystal monomer in the liquid crystalsolution was vertically oriented. The liquid crystal transition point atwhich the color of the film formed of the liquid crystal solutionchanged from white to transparent was visually observed, so theorientation of a liquid crystal molecule was confirmed.

Next, in the nitrogen atmosphere, the liquid crystal layer oriented onthe glass base material was irradiated with ultraviolet light of 20mW/cm² for 10 seconds by means of an ultraviolet irradiation devicehaving an ultra-high pressure mercury lamp (trade name “TOSCURE 751”manufactured by HARISON TOSHIBA LIGHTING Corp.) so that the liquidcrystal monomer molecules constituting the liquid crystal layer werethree-dimensionally crosslinked. Thus, a base material 1 provided with abirefringence layer was formed.

After that, the base material 1 was subjected to a baking treatment at230° C. for 1 hour in order to improve the heat resistance andadhesiveness of the birefringence layer in the base material 1.

Finally, the surface of the base material 1 (surface opposite to theglass base material) was etched through plasma dry etching, so a surfacelayer was removed from the surface by a depth of about 1,000 Å. Thus,Example 1 as the optical element of the present invention was produced.The plasma dry etching was performed by means of a DEA-506T devicemanufactured by ANELVA Corporation and an oxygen gas having a flow rateof 60 sccm and a gas pressure of 30 mTorr under the conditions includingan RF power of 500 W and an etching time of 3 minutes.

Example 2

A base material 2 was formed in the same manner as in Example 1, andExample 2 was produced in the same manner as in Example 1 except thatthe surface of the base material 2 (surface opposite to the glass basematerial) was ground by means of a grinding attachment by a depth of1,000 Å.

Comparative Example 1

A base material 3 provided with a vertical alignment layer and abirefringence layer on the upper surface of a glass base material wasformed in the same manner as in Example 1, and was defined asComparative Example 1.

(Evaluation 1)

The haze in each of Example 1, Example 2, and Comparative Example 1 thusobtained was measured. The haze was measured in conformance with JIS K7136 by installing each optical element in a haze measuring machine. An“NDH-2000” manufactured by NIPPON DENSHOKU was used as the hazemeasuring machine.

As a result, the haze of each of the optical elements of Examples 1 and2 was lower than 0.1, and showed a value as low as 0.06. In contrast,the haze of Comparative Example 1 was much larger than 0.1, and showedan extremely high value (1.0).

(Evaluation 2)

The structure of a liquid crystal layer to be formed on the surfaceopposite to a base material of Examples 1 and 2 was confirmed by meansof the following evaluation method. A method involving measuring: thephase difference in the thickness direction (direction slanted from afilm normal direction by 45°) of an optical element obtained by etchingthe surface opposite to the base material; and a haze distribution wasadopted as the evaluation method. In addition, the mixed state ofimpurities in an etched region was analyzed. Furthermore, a polarizedstate was confirmed by rotation under polarizing plate crossed nicol.The above etching was performed by means of a DEA-506T devicemanufactured by ANELVA Corporation and oxygen as an etching gas underthe conditions including an etching gas flow rate of 60 sccm, an etchinggas pressure of 30 mTorr, and an electric power to be applied of 500 W.A TOF-SIMS manufactured by ULVAC-PHI, INC. was used for an impuritymixing analysis test.

As a result, neither phase difference nor haze changed up to a depth ofabout 1,200 Å from the surface of each of Examples 1 and 2 even afteretching. In addition, the impurity mixed state of the region wasinvestigated. As a result, no impurity was detected. This resultconfirmed that, on each of the surfaces in Examples 1 and 2, no additivelayer to be acknowledged as an impurity was present and a birefringencelayer was exposed to the surface of the optical element.

Meanwhile, Comparative Example 1 was evaluated in the same manner asthat described above. As a result, up to a depth of about 1,000 Å fromthe surface, a haze was extremely high, and the mixing of impurities wasconfirmed. This confirmed that a layer different from a liquid crystallayer, that is, an additive layer was present.

The above results confirmed that the haze of the optical element ofComparative Example 1 in which the additive layer is present on theupper surface of the optical element shows a high value, but the haze ofeach of Examples 1 and 2 in each of which the additive layer is removedshows an extremely low value (0.1 or less).

Example 3

The liquid crystal display device shown in FIG. 9B was produced as aliquid crystal display device using the optical element of the presentinvention, and was defined as Example 3.

The optical element of the present invention was formed in the samemanner as in Example 1 except that a coloring layer was formed between aglass base material washed through a pretreatment and a verticalalignment layer in order to produce Example 3.

To form the above coloring layer, at first, a photoresist for a BMprepared as described above was applied to the upper surface of theglass base material by means of a spin coating method to have athickness of 1.2 μm, and the whole was pre-baked at 80° C. for 3minutes. Then, the resultant was exposed to light (100 mJ/cm²) by meansof a mask formed into a predetermined pattern. Subsequently, theresultant was subjected to spray development with a 0.05% aqueoussolution of KOH for 50 seconds. After that, the resultant was post-bakedat 230° C. for 30 minutes to prepare a BM substrate.

Next, a red (R) pigment-dispersed photoresist was applied to the aboveBM substrate by means of a spin coating method, and the whole waspre-baked at 90° C. for 3 minutes. Then, the resultant was subjected toalignment exposure (100 mJ/cm²) by means of a photomask for apredetermined coloring pattern. Subsequently, the resultant wassubjected to spray development with a 0.1% aqueous solution of KOH for50 seconds. After that, the resultant was post-baked at 230° C. for 30minutes. As a result, a red (R) coloring pixel pattern having athickness of 1.2 μm was formed at a predetermined position with respectto the BM pattern.

Subsequently, a green (G) coloring pixel pattern having a thickness of1.2 μm was formed by means of the same method as the method of formingthe above red (R) coloring pixel pattern and under the same conditionsas those of the above method.

Furthermore, a blue (B) coloring pixel pattern having a thickness of 1.2μm was formed by means of the same method as the method of forming theabove red (R) coloring pixel pattern and under the same conditions asthose of the above method.

Thus, the coloring layer constituted by the BM, the red coloring pixel,the green coloring pixel, and the blue coloring pixel formed on thesubstrate was formed.

Next, a base material 4 including a vertical alignment layer and abirefringence layer was formed on the upper surface of the coloringlayer in the same manner as in Example 1.

After that, the base material 4 was baked in the same manner as inExample 1.

Subsequently, a surface layer was removed by a depth of about 1,000 Åfrom the surface of the base material 4 (surface opposite to the glassbase material) in the same manner as in the base material 1 inExample 1. As a result, an optical element of the present inventionincluding a coloring layer was produced.

Next, an acrylic resin was formed into a protective layer having athickness of 1.0 μm by means of a spin coating method on the uppersurface of the birefringence layer in the optical element obtained byremoving the surface layer of the base material 4. Furthermore, indiumtin oxide (ITO) was formed into a film-like common electrode portion onthe upper surface of the protective layer. Meanwhile, thin-filmtransistors (TFT's) were formed at multiple predetermined sites on thesame glass substrate as that used for the base material 4. Then, atransparent pixel electrode was formed of indium tin oxide (ITO) so asto be connected to the drain electrode of each TFT, thereby a counterelectrode substrate was produced.

Then, a polyimide resin coating was applied in such a manner that eachof the surface of the transparent common electrode and the surface ofthe transparent pixel electrode would be covered with the coating, andwas dried to provide alignment layers (each having a thickness of 0.07μm). Then, the resultant was subjected to an orientation treatment.Subsequently, both substrates were opposed to each other in such amanner that those alignment layers would face each other. A spacebetween both substrates was sealed with a sealing member. Liquid crystal(MLC-6846-000 manufactured by Merck Ltd., Japan) was injected into thesealed space, and the inlet was sealed. Thus, a liquid crystal displaydevice was produced and defined as Example 3.

Comparative Example 2

A liquid crystal display device was produced in the same manner as inExample 3 except that a base material 5 in which the upper surface of abirefringence layer was not removed (that is, an additive layer waspresent on the upper surface of the birefringence layer) was usedinstead of the base material 4 having the coloring layer formed inExample 3, and the device was defined as Comparative Example 2.

(Evaluation 3)

The contrast performance of each of the liquid crystal display devicesof Example 3 and Comparative Example 2 was measured as described below.

Contrast performance measurement involves: forming a state where lightthat had passed through a liquid crystal layer in the above produceddevice could easily pass through a polarizing plate (light state) and astate where the light could not easily pass through the polarizing plate(dark state); and measuring the brightness of the light that had passedthrough the liquid crystal layer and the polarizing plate to traveltoward the outside for each of the light state and the dark state. Then,a value obtained by dividing the brightness in the light state by thebrightness in the dark state was used as an index showing contrastperformance.

As a result, the contrast performance of Example 3 was 750. This valuewas sufficient for a liquid crystal display device. On the other hand,the performance of Comparative Example 2 was 450. This value was muchlower than that of Example 3.

1. An optical element comprising: a base material having lighttransmittance; and a birefringence functional layer including at least abirefringence layer, wherein: the birefringence layer has a structureobtained by fixing liquid crystal monomers each having a polymerizablegroup at a terminal thereof in a state where the monomers arehomeotropically oriented; the birefringence layer contains an additivefor promoting the homeotropic orientation of the liquid crystal monomer;and no additive layer constituted by the additive is present on theupper surface of the birefringence layer.
 2. An optical elementaccording to claim 1, wherein the birefringence functional layercomprises a vertical alignment layer formed on an upper surface of thebase material and the birefringence layer formed on an upper surface ofthe vertical alignment layer.
 3. An optical element according to claim2, wherein at least one component for promoting homeotropic orientationof a liquid crystal monomer in the vertical alignment layer is used forthe additive.
 4. An optical element according to claim 1, wherein theliquid crystal monomers constituting the birefringence layer areoriented while showing a substantially uniform tilt angle.
 5. An opticalelement according to claim 1, wherein a coloring layer is formed on oneof a position between the base material and the birefringence functionallayer and a position on an upper surface of the birefringence functionallayer.
 6. A member for a liquid crystal display device comprising: twolaminated structures each including a layer having light transmittance;and a liquid crystal layer in which liquid crystal is sealed, the liquidcrystal layer being interposed between the two laminated structures,wherein the optical element according to claim 1 is formed in at leastone of the laminated structures.
 7. A member for a liquid crystaldisplay device according to claim 6, wherein the birefringence layer inthe optical element is formed to be positioned on a side of the liquidcrystal layer in the member for a liquid crystal display device.
 8. Aliquid crystal display device having a multilayer structure, the devicecomprising: polarizing plates with liquid crystal interposedtherebetween; and a layer composed of an electrode portion for changingorientation of a liquid crystal layer through application of a voltage,wherein the member for a liquid crystal display device according toclaim 6 is used.
 9. A liquid crystal display device having a multilayerstructure, the device comprising: polarizing plates with liquid crystalinterposed therebetween; and a layer composed of an electrode portionfor changing orientation of a liquid crystal layer through applicationof a voltage, wherein the member for a liquid crystal display deviceaccording to claim 7 is used.